(1) Field of the Invention
The present invention relates to an apparatus for processing photosensitive materials, such as an automatic film developing machine and a photosensitive printing plate processing apparatus. More particularly, the invention relates to a method of controlling a temperature within the drying section of such an apparatus. According to the invention, the drying section is maintained at a low temperature during a standby period (when photosensitive material is not present in the apparatus). To dry the photosensitive material, the temperature of the drying section is raised to a predetermined level. The invention achieves energy savings and reduces costs.
(2) Description of the Prior Art
FIG. 3 of the accompanying drawing schematically shows a photosensitive processing apparatus and, in particular, an automatic film developing machine.
This machine comprises a main frame 1 housing a developing tank 2, a fixing tank 3 and a rinsing tank 4 arranged in series. An exposed photographic film is transported by an unillustrated transport member along a path indicated by a chain dot line and arrows through the tanks for developing, fixing and rinsing. The main frame 1 further houses a drying section 5 disposed on the film path downstream of the tanks. The drying section 5 directs hot air heated by heaters 6 to the film to evaporate water and to dry the film. The dried film is delivered to a receptacle 7. A lid 8 including an exhaust duct 9 is mounted on top of the main frame 1.
The drying section 5 includes a drying temperature sensor, not shown, for communicating on actually measured drying temperature to a control section 11. The control section 11 carries out temperature control by turning the heaters 6 on and off in response to the actually measured drying temperature.
In recent years, measures for saving energy or resources have been taken with such an automatic film developing machine. These measures include (1) reducing the drive rate of the transport member and (2) stopping delivery of water to the rinsing tank 4 during a standby period when there is no film to be processed.
The drying section 5 includes powerful electric heaters and large blowers in order to dry the film reliably. The heaters and the blowers consume more electricity than any other part of the machine. Energy is saved by stopping these heaters and blowers. Thus, it has been conventional practice to operate the heaters at a low temperature or to stop the blowers during a standby period.
A unit for changing these devices from a standby state to an operative state comprises a film detector 10 such as a photoelectric switch, a microswitch or the like mounted at a film inlet of the developing machine. The film detector 10 detects a leading end of the entering film and outputs a detection signal which forms a basis for controlling the heaters and blowers.
Energy is effectively saved by maintaining the temperature in the drying section 5 at a preheating temperature during the standby period (hereinafter referred to as "standby temperature") which is lower than a predetermined operating temperature for actually drying the film. Conventionally, however, the standby temperature is simply set at a level which is lower than the operating temperature by a fixed amount. This practice has disadvantages 7 as described below.
When the heaters 6 are continuously electrified after the drying section 5 has been maintained at the standby temperature, the temperature of the drying section 5 does not instantly rise to the operating temperature. The temperature rises to the operating temperature gradually, describing a relatively gentle curve as shown in FIG. 2, for example.
On the other hand, the developing period for the film under treatment, namely the time required for the film to travel through the developing solution in the developing tank 2, is variable and depends on several factors such as the type of film, the type of processing solution, and the film exposing conditions. The film is transported at low speed to extend the developing period. The film is transported at high speed to shorten the developing period. Consequently, the time from the point of time at which the film is fed into the machine (and the heaters 6 begin to be electrified continuously in response to the signal of detector 10) until the point of time at which the film reaches the drying section 5 is variable.
The difference between the standby temperature and the operating temperature could be large if film is transported only at low speed. However, with a large difference, the drying section 5 can not be heated to the operating temperature in time to properly dry film transported at high speed. Thus, high speed film would be insufficiently dried. Conventionally, therefore, the standby temperature is set to a somewhat higher level so as to be suited for the situation in which film is transported at the highest speed and thus for the shortest developing time) possible for the machine. This practice unsatisfactorily wastes energy.
Further, when the standby temperature is set to a lower level than the operating temperature by a fixed amount, the time taken to reach the operating temperature depends on the operating temperature. That is, when the heaters 6 are continuously electrified, the temperature in the drying section 5 rises rapidly in the low temperature region and slowly in the high temperature region as seen in FIG. 2. Thus, the time required for the standby temperature to rise to the operating temperature depends on the level selected for the operating temperature.